Steady and Unsteady Force and Moment Data on a DARPA2 Submarine
Steady and unsteady force and moment experiments were conducted in the Virginia Tech Stability wind tunnel using the Dynamic Plunge-Pitch-Roll (DyPPiR) model mount to perform rapid time-dependent,high-excursion maneuvers. The experiments were performed for a DARPA2 submarine model using three widely spaced 2-force-component loadcells and three tri-axial accelerometers to extract the aerodynamic loads.
The DARPA2 model was tested with different body configurations in two different test sections. The body configurations for both the steady and unsteady experiments were the bare body hull, body with sail, body with stern appendages, and body with sail and stern appendages. Tests were done using trips on the bow and sail and with no trips. The bare hull configuration with no trips was the only body configuration tested in the six-foot-square test section with solid walls. All body configurations were tested in the six-foot-square test section with slotted walls that were used to reduce the blockage effects produced by the DyPPiR and model.
The steady experiments were performed over a range of angles of attack and roll positions. Data were acquired through the series of angles the body encountered during the unsteady testing (-26° < ± <+26° ). The data for the tripped bare hull gave symmetric results while the data acquired for the bare hull with no trips did not. In the unsteady experiments the model was pitched in ramp maneuvers about the 1/4 chord location of the sail from 0° to -25° and from +25° to 0° in 0.3 seconds. Sine wave maneuvers at 3 Hz were also performed, plunging the model up and down with an amplitude of ±0.375 inches. The steady data agreed within uncertainties with previous data that were limited to the David Taylor Research Center (DTRC). There was a higher level of confidence in the steady data taken with trips due to the symmetry of the data. Effects of the sail and/or stern appendages were studied using the steady and unsteady data, but no quantitative value could be calculated due to the uncertainties. The unsteady data were modeled with a quasi-steady time-lag model, and all the unsteady data were found to lead the quasi-steady data. The unsteady data did have oscillations, but the overall aerodynamic trend was still present. The uncertainties were too large to discuss effects of any appendages, however.